Video images are often provided as ITU-R 601 compliant images (e.g., NTSC with 704×480 pixels) that have 13.5 MHz display sample rate. These video images typically have oblong pixels. On the other hand, graphics images are often provided with square pixels with a sample rate of 12.27 MHz. For example, a typical graphics image may have 640×480 pixels. In a video and graphics system, video and graphics are often overlaid on top of each other to provide a blended image. It is desirable to combine the video and graphics in such a way that both retain their individual and correct pixel aspect ratios. It is also desirable to perform this function without modifying the video samples or changing the sample rate of the video. Blending of video and graphics is often difficult due to their different image sizes and pixel aspect ratios.
Prior attempts to implement similar functions have suffered from problems. For example, some previous designs produced visual artifacts in the resulting displayed graphics, such as aliasing, blurring, or ringing. Others, in addition to these problems, have slow performance due to their additional accesses to shared memory.
Therefore, it is desirable to provide a method and apparatus for overlaying video and graphics to generate a blended image without appreciable image quality degradation, in such a way that both retain their individual and correct pixel aspect ratios without modifying the video samples or changing the video sample rate.